Health insurance is a type of coverage that pays for medical and surgical expenses incurred by the insured individual. It is a contract between the policyholder (the person who buys the insurance) and the insurance company, where the insurer agrees to cover the costs of certain healthcare services in exchange for regular premium payments.

Here are some key points to understand about health insurance:

1. **Premium**: This is the amount you pay to the insurance company on a regular basis, typically monthly or annually, to maintain your health insurance coverage.

2. **Coverage**: Health insurance plans vary in terms of what they cover. Common covered services include doctor visits, hospital stays, prescription medications, preventive care, and some types of surgery. The specific services covered will depend on the plan you choose.

3. **Deductible**: This is the amount you must pay out of pocket for covered healthcare services before your insurance plan starts to pay. For example, if you have a $1,000 deductible, you'll need to pay the first $1,000 of covered medical expenses before your insurance kicks in.

4. **Co-payments and Co-insurance**: After you meet your deductible, you may still be responsible for a portion of your healthcare costs. Co-payments are fixed amounts you pay for certain services (e.g., $20 for a doctor's visit), while co-insurance is a percentage of the cost you must cover (e.g., 20% of the bill).

5. **Network**: Many health insurance plans have networks of doctors, hospitals, and other healthcare providers. Staying within your plan's network can often result in lower out-of-pocket costs.

6. **Out-of-Pocket Maximum/Limit**: This is the maximum amount you will have to pay for covered healthcare services in a plan year. Once you reach this limit, your insurance company will cover 100% of covered expenses.

7. **Preventive Care**: Most health insurance plans are required to cover certain preventive services at no cost to you. This can include vaccinations, screenings, and wellness visits.

8. **Types of Plans**: There are various types of health insurance plans, including Health Maintenance Organization (HMO), Preferred Provider Organization (PPO), Exclusive Provider Organization (EPO), and Point of Service (POS) plans. Each has its own rules and limitations.

9. **Open Enrollment**: In many countries, there's a specific period, usually once a year, when individuals can enroll in or make changes to their health insurance plans. Outside of this period, you may need to qualify for a special enrollment period to make changes.

10. **Government Programs**: Some countries, like the United States, offer government-sponsored health insurance programs such as Medicare (for seniors and certain disabled individuals) and Medicaid (for low-income individuals and families).

Having health insurance can provide financial protection in case of unexpected medical expenses and help ensure that you have access to necessary healthcare services. It's essential to carefully review and compare different health insurance plans to find one that meets your needs and fits your budget.